Light-emitting devices such as lasers are useful for optical signal generation in optoelectronic networks. Often, light from a laser is modulated to encode data or information onto the signal. One approach to modulating laser light is electro-absorption modulation (EAM), in which an electric potential applied across the modulator either allows light to pass through the modulator or creates a destructive interference pattern in the light passing into the modulator, thereby turning the light signal off.
To reduce power, the optical signal output by the electro-absorption modulated laser (EML) can be transmitted differentially. Differential modulation using electro-absorption modulators has either used discrete laser and modulator devices, or, if integrated on a single chip, the modulator section and the laser section generally have common electrical contact points. The common electrical contact points typically include the cathode, n-contact, and/or ground. The anodes or p-contacts of the laser section and modulator section are typically electrically isolated.
However, in a multi-channel transmitter (i.e., having a plurality of paired lasers and modulators), providing a common ground contact for the modulators does not allow for driving each modulator with a differential signal. Differential modulation has typically involved either a shared contact between the modulator section and laser section, or a laser that is not integrated onto the modulator chip.
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